Conventionally, many techniques for producing adamantane by isomerizing tetrahydrodicyclopentadiene under an acid catalyst are known (see, for example, Patent Documents 1 and 2). Especially, techniques for producing adamantane by isomerizing tetrahydrodicyclopentadiene using an HF catalyst and a BF3 catalyst are well known (see, for example, Patent Documents 3 and 4, and Non-patent Document 1). However, the conventional techniques of using an HF catalyst and a BF3 catalyst have the following defects. Where a large amount of adamantane is generated, adamantane is deposited as a solid. In order to obtain adamantane as a solid, the reactor needs to be opened. In the case where the reactor should be prevented from being opened, the deposited adamantane needs to be dissolved in a solvent to be formed into a solution, and so use of a solvent is unavoidable.
Patent Document 1: Japanese Patent Publication for Opposition No. S52-2909
Patent Document 2: Japanese Patent Publication for Opposition No. H03-031182
Patent Document 3: Japanese Patent Publication for Opposition No. S55-38935
Patent Document 4: Japanese Laid-Open Patent Publication No. 2001-151705
Non-patent Document 1: J. Org. Chem., Vol. 51, No. 26, 1986